On the viability of holistic cosmic-ray source models

We consider the energy spectrum of cosmic-rays (CRs) from a purely phenomenological point of view and investigate the possibility that they all be produced by the same type of sources with a single power-law spectrum, in E^{-x}, from thermal to ultra-high energies. We show that the relative fluxes of the Galactic (GCR) and extra-galactic (EGCR) components are compatible with such a holistic model, provided that the index of the source spectrum be x \simeq 2.23\pm 0.07. This is compatible with the best-fit indices for both GCRs and EGCRs, assuming that their source composition is the same, which is indeed the case in a holistic model. It is also compatible with theoretical expectations for particle acceleration at relativistic shocks.Comment: 5 pages, 1 figure, Accepted for publication in Astronomy and Astrophysic

Experimental conditions to suppress edge localised modes by magnetic perturbations in the ASDEX Upgrade tokamak

Access conditions for full suppression of Edge Localised Modes (ELMs) by Magnetic Perturbations (MP) in low density high confinement mode (H-mode) plasmas are studied in the ASDEX Upgrade tokamak. The main empirical requirements for full ELM suppression in our experiments are: 1. The poloidal spectrum of the MP must be aligned for best plasma response from weakly stable kink-modes, which amplify the perturbation, 2. The plasma edge density must be below a critical value, $3.3 \times 10^{19}$~m$^{-3}$. The edge collisionality is in the range $\nu^*_i = 0.15-0.42$ (ions) and $\nu^*_e = 0.15-0.25$ (electrons). However, our data does not show that the edge collisionality is the critical parameter that governs access to ELM suppression. 3. The pedestal pressure must be kept sufficiently low to avoid destabilisation of small ELMs. This requirement implies a systematic reduction of pedestal pressure of typically 30\% compared to unmitigated ELMy H-mode in otherwise similar plasmas. 4. The edge safety factor $q_{95}$ lies within a certain window. Within the range probed so far, $q_{95}=3.5-4.2$, one such window, $q_{95}=3.57-3.95$ has been identified. Within the range of plasma rotation encountered so far, no apparent threshold of plasma rotation for ELM suppression is found. This includes cases with large cross field electron flow in the entire pedestal region, for which two-fluid MHD models predict that the resistive plasma response to the applied MP is shielded

Genomic and transcriptomic signals of thermal tolerance in heat-tolerant corals (Platygyra daedalea) of the Arabian/Persian Gulf

© 2018 John Wiley & Sons Ltd Scleractinian corals occur in tropical regions near their upper thermal limits and are severely threatened by rising ocean temperatures. However, several recent studies have shown coral populations can harbour genetic variation in thermal tolerance. Here, we have extended these approaches to study heat tolerance of corals in the Persian/Arabian Gulf, where heat-tolerant local populations experience extreme summer temperatures (up to 36°C). To evaluate whether selection has depleted genetic variation in thermal tolerance, estimate potential future adaptive responses and understand the functional basis for these corals’ unusual heat tolerance, we conducted controlled crosses in the Gulf coral Platygyra daedalea. Heat tolerance is highly heritable in this population (h 2 = 0.487–0.748), suggesting substantial potential for adaptive responses to selection for elevated temperatures. To identify genetic markers associated with this variation, we conducted genomewide SNP genotyping in parental corals and tested for relationships between paternal genotype and offspring thermal tolerance. Resulting multilocus SNP genotypes explained a large fraction of variation in thermal tolerance in these crosses (69%). To investigate the functional basis of these differences in thermal tolerance, we profiled transcriptional responses in tolerant and susceptible families, revealing substantial sire effects on transcriptional responses to thermal stress. We also studied sequence variation in these expressed sequences, identifying alleles and functional groups of differentially expressed genes associated with thermal tolerance. Our findings demonstrate that corals in this population harbour extensive genetic variation in thermal tolerance, and heat-tolerant phenotypes differ in both gene sequences and transcriptional stress responses from their susceptible counterparts

Development of chick embryo explant cultures as an assay system to test mammalian stem cell migration and differentiation after transplantation

Abstract only availableStem cells are undifferentiated cells capable of achieving multiple developmental fates. The embryonic stem (ES) cell can differentiate into all cells of the body. Our stem cell research focuses on the repair and/or renewal of cells in the central nervous system with potential applications for treatment of such diseases as Parkinson's disease, ALS, Alzhiemers disease, Batten's disease, as well as other neurodegenerative disorders and injuries to the CNS. An important problem is to determine the potential of stem cells to achieve various fates after transplantation. In the present study, we developed the chick embryo explant culture as an assay system to test the ability of mouse embryonic stem cells to migrate and differentiate after transplantation. The focus of this study was to monitor the survival, migration, and incorporation of the mouse ES cells after transplantation into chick embryos and to develop an explant culture method. The explant cultures will enable repeated viewing of transplanted stem cells at various time post-transplantation. Initially to establish chick embryo explants, chicken embryos were excised from the yolk at stage 8 and transferred to agar/albumen culture dishes containing antibiotics. The chick embryos explants were incubated at 37oC in a humidified chamber to continue growth and development, and explants were viewed multiple times. To date, chick embryos survived up to 47 hours after explantation. Successful explants were obtained as determined by normal embryonic development and the presence of a normal heartbeat. For stem cell transplant experiments, green fluorescent protein (GFP)-expressing mouse ES cells were transplanted into the head region of stage 10 chick embryos while the embryos were still in the egg (i.e., in ovo). Immediately following transplantation, explant cultures were established and embryonic development was allowed to proceed for up to 28 hours (~stage 15-16). The embryos were screened using a fluorescence microscope to test for the presence and fate of transplanted mouse ES cells. Ten micrometers thick transverse sections of the embryos were examined and GFP-expressing cells were found in the lower head region around the neural tube. The transplanted ES cells appeared to contribute to embryonic mesoderm. Future experiments will test whether transplanted stem cells can incorporate into the neural tube and differentiate into neural cells.NSF-REU Biology & Biochemistr

A near-infrared variability study in the cloud IC1396W: low star-forming efficiency and two new eclipsing binaries

Identifying the population of young stellar objects (YSOs) in high extinction regions is a prerequisite for studies of star formation. This task is not trivial, as reddened background objects can be indistinguishable from YSOs in near-infrared colour-colour diagrams. Here we combine deep JHK photometry with J- and K-band lightcurves, obtained with UKIRT/WFCAM, to explore the YSO population in the dark cloud IC1396W. We demonstrate that a colour-variability criterion can provide useful constraints on the star forming activity in embedded regions. For IC1396W we find that a near-infrared colour analysis alone vastly overestimates the number of YSOs. In total, the globule probably harbours not more than ten YSOs, among them a system of two young stars embedded in a small (~10000 AU) reflection nebula. This translates into a star forming efficiency SFE of ~1%, which is low compared with nearby more massive star forming regions, but similar to less massive globules. We confirm that IC1396W is likely associated with the IC1396 HII region. One possible explanation for the low SFE is the relatively large distance to the ionizing O-star in the central part of IC1396. Serendipitously, our variability campaign yields two new eclipsing binaries, and eight periodic variables, most of them with the characteristics of contact binaries.Comment: 13 pages, 10 figures, MNRAS, in pres

Near Real-Time Use of Optical Remote Sensing and Synthetic Aperture Radar for Response to Central U.S. Flooding in Late April-Early May 2017

No abstract availabl